1. Field of the Invention
The present invention relates to a seal chain used as a driving chain for transportation machines such as a motor cycle and of general industrial machines or as a conveyer chain for a conveyor or the like and more specifically to a seal chain and a manufacturing method of the same using a sealing member whose cross-section is approximately in a shape of a “plus” sign in a natural condition.
2. Description of Related Art
Conventionally, the present applicant has proposed a method for manufacturing a seal chain using a ringed sealing member having a lip portion that extends in an inner diametric direction thereof in a natural condition and being attached between an inner link plate and an outer link plate such that it is twisted at the fulcrum of the lip portion as disclosed in Japanese Patent Publication No. 1994-48038 (JA-B-H06-43038). FIGS. 6A through 6C show its manufacturing method. As shown in FIG. 6A at first, a first lip portion 3a of the sealing member 3 is positioned between an edge of a bush head portion 7a and the outer link plate 8 and then the outer link plate 8 is assembled provisionally with a pin 2 while leaving a predetermined space c from the sealing member 3. The seal chain is then soaked in fluid grease, for example, in this state to feed the grease between the pin 2 and a bush 7 within the sealing member 3. Then, the outer link plate 8 is pressed in a direction of an arrow shown in FIG. 6B. As the outer link plate 8 is pressed at this time, the outer link plate 8 contacts with the sealing member 3. When the outer link plate 8 moves further in the direction of the arrow in a state in which the first lip portion 3a of the sealing member 3 abuts against the edge of the head portion 7a of the bush 7, the sealing member 3 is twisted as shown by arrows in FIG. 6C at the fulcrum of the abutting part.
Thereby, the sealing member 3 is positioned such that the first lip portion 3a abuts against an outer peripheral face of the edge of the bush head portion 7a and against the outer link plate 8, a third lip portion 3c abuts against the outer link plate 8, a fourth lip portion 3d abuts against the inner link plate 6 and a second lip portion 3b abuts against the inner link plate 6. That is, the sealing member 3 is sandwiched between the two link plates 6 and 8 in a shape of an “X” in section. The sealing member 3 is attached as described above on the sides of the bush 7 and the edge of the pin 2 is caulked to stop the outer link plate 8. The seal chain 1 is thus completed.
FIGS. 7A and 7B are section views showing different types of sealing member 3 in a natural state. The sealing member 31 in FIG. 7A has a wide and semicircular first lip portion 31a extending in an inner diametric direction thereof, a second lip portion 31b having the same width with the first lip portion 31a and extending in an outer diametric direction thereof and third and fourth narrow lip portions 31c and 31d extending in both transverse directions from the first and second lip portions 31a and 31b. The sealing member 31 is formed approximately in a shape of a “plus” in section as a whole. An edge portion of the first lip portion 31a is formed into a shape of circular arc r1a having a semicircular curve and parts connecting the respective lip portions are formed by circular arcs of predetermined r.
The sealing member 32 in FIG. 7B has a first lip portion 32a extending in an inner diametric direction and having an approximately circular shape in section and a second lip portion 32b, a third lip portion 32c and a fourth lip portion 32d extending in an outer diametric direction and in both transverse directions and having the same width, respectively. Accordingly, the sealing member 32 is formed such that the first lip portion 32a has a shape of circular arc r2a, parts connecting the first lip portion 32a with the lip portions 32c and 32d are formed by concaved circular arcs r′ and parts connecting the second lip portion 32b with the third and fourth lip portions 32c and 32d are formed by predetermined circular arcs r.
The third and fourth lip portions 31c and 31d as well as the third and fourth lip portions 32c and 32d of the conventional sealing members 31 and 32 have the same width b1 and b2, respectively, and extend in the transverse direction by a predetermined length from the position where they are connected with the first and second lip portions 31a and 31b or 32a and 32b with the relatively small circular arcs r and r′. They are formed almost symmetrically with respect to a center line a-a.
Because the sealing member 31 or 32 is interposed between the inner and outer link plates 6 and 8 in the seal chain 1, a clearance between the inner and outer link plates 6 and 8 must be large as compared to a non-seal chain having no seal. Accordingly, the seal chain described above requires a longer pin in order to meet with the large clearance and hence the pin is susceptible to being bent. Then, the tensile strength of the chain becomes small as compared to the non-seal chain even when a pin having the same diameter and a same link plate are used.
Although it is necessary to reduce the clearance between the inner and outer link plates 6 and 8 in order to increase the strength of the seal chain, the sealing member is exhausted quickly if a cross-sectional area of the sealing member is reduced. Then, pressure of the lip portions against the plate is weakened and lubricant oil leaks, ending up dropping abrasion resistance of the chain and shortening the life of the chain.
In the seal chain 1 described above, each lip portion contacts with the inner link plate, the outer link plate or the bush head portion in the state in which the sealing member is sandwiched between the inner and link plates 6 and 8 such that the sealing member surrounds the bush head portion 7a. Then, recesses between the lip portions become oil reservoirs, thus retaining the durability and flexibility of the chain. In the case of the sealing member 31 in FIG. 7A, length z1 of a diagonal line of a central base portion 31e is long, so that the lip portions having the recesses, i.e., the oil reservoirs described above, cannot be effectively formed when improving the strength of the chain by reducing the clearance between the outer and inner link plates. Then, it becomes unable to display the particular effects of a seal ring having the shape of X in section of reducing transmission loss of the chain while maintaining the durability of the chain and improving its flexibility.
In case of the sealing member 32 in FIG. 7B, a cross-sectional area of a central base portion 32e becomes small if the shape of the sealing member is analogously reduced corresponding to the reduction of the clearance and the problem of dropping the abrasion resistance of the chain described above becomes remarkable.
The sealing member 32 (although the sealing member 32 will be explained below, the same applies also to the sealing member 31) is twisted as shown by a dotted chain line in FIG. 8 when the first lip portion 32a abuts against the edge f of the bush head portion 7a. At this time, the third lip portion 32c is pressed by the movement of the outer link plate 8, the fourth lip portion 32d moves along an outer circumferential face of the bush head portion 7a and the first lip portion 32a is twisted while turning at the fulcrum of a contact point of the edge f of the bush head portion 7a and the first lip portion 32a. Accordingly, a suitable gap g is necessary between the edge of the fourth lip portion 32d and the inner link plate 6 in order for the sealing member 32 to turn. Meanwhile, as for length h of head of the bush head portion 7a, even when the clearance i between the inner and outer link plates is to be reduced when the chain is assembled, a gap d (=i−h) between the edge f of the bush head portion and the outer link plate 8 cannot be reduced in order to avoid the metals contacting each other, so that the length h of the head must be reduced if the clearance is to be reduced. Accordingly, as the clearance is reduced in order to improve the strength of the chain, the length h of the bush head portion 7a cannot but be shortened and the gap g suitable for turning the sealing member 32 as described above cannot but be also reduced. Then, one end j1 of the third lip portion 32c must be moved to j2 and energy for drawing the third lip portion 32c is required at this time in order to move the outer link plate from 81 to position of 82 and to turn and attach the sealing member 32 at normal position as the X-shaped sealing member (ring) as indicted by a chain line.
In a case of the shape of the sealing member 32 (the same applies also to the sealing member 31) having the third lip portion 32c having the same width b2 as described above, the pressure from the outer link plate 81 acts as a parallel distributed load on the third lip portion 32c and its resultant force acts on the center part of the sealing member 32 as indicated by an arrow F. However, a turning moment of the sealing member 32 based on this resultant force is relatively small and when the gap g is small, there is a case when an edge face k1 of the fourth lip portion 32d contacts the inner link plate 6, as indicated by k2, before the sealing member 32 turns going against the energy of drawing the third lip portion 32c. Then, as indicated by the sealing member 32′, the edge faces k2 and s2 of the third and fourth lip portions 32c and 32d are pressed against the inner and outer link plates 6 and 8 before the sealing member is fully turned. At this time, although the first lip portion 32a of the sealing member abuts against the head face f of the bush head portion 7a and the sealing member 32 generates moment at the fulcrum of the abutment point, the first lip portion 32a tends to be deformed and a force twisting the sealing member 32 is substantially generated based on turning moment F·1 at a fulcrum e generated in the central base portion 32e. Then, as for the third and fourth lip portions 32c and 32d having the same width b2 from their edge face to the central base portion 32e, the turning moment (F·1) to the fulcrum e acting on the central base portion 32e of the sealing member 32′ is very small, the sealing member 32′ is squeezed in the shape of a “plus” between the both inner and outer link plates 6 and 8, reaction force acting from the third and fourth lip portions 32c and 32d to the inner and outer link plates 6 and 8 is balanced on the inner and outer diametric sides in this state and the sealing member is stabilized in the shape of a “plus”. If such sealing members 32′ exist even in a small number, it becomes impossible to obtain a seal chain having a sealing member that has the particular shape of an “X” by which the functions of retaining the abrasion resistance of the chain owing to the sealing function described above and of retaining the flexibility of the chain owing to the lip portions are well balanced.